SOUTH AFRICAN TERMITES. 41 



the resistor ; from here it passes diagonally to the tip of the 

 lever ; from tlie lever it extends outwards slightly and is 

 fixed to the tergite just Avithin the cephalo-lateral corner, on 

 the line where the chitinisation begins to be less dense. The 

 strap of muscle from chin-plate to lever contracts and draws 

 the lever towards and somewhat aci^oss the foot of the resister. 

 The resister and lever are linked by a tlexible band which 

 acts as a fulcrum but not as a spring, the lumen being 

 opened by the strap of muscle extending from the lever to the 

 tergite. 



The transitional conditions between the second and the 

 third stage differ mainly from the second in the noticeable 

 decrease in the length of the atrium. The shortening of the 

 atrium is a gradual process due to the throwing off of the rim 

 of the pore at each ecdj^sis. Fig. 30 shows a spiracle about 

 to enter upon the third stage, and a new rim {nr.) is seen in 

 the course of formation behind the pore (_pr.). Another 

 feature is the marked differentiation of the chin-plate. 



The spiracles IV to X of the male may be taken as repre- 

 senting the third stage. This form is shown, fig. 31a, from 

 the visceral aspect, and the attitude of the lever when open 

 and shut is indicated below the fragment of the trachelos. 

 In the illustration it will be noticed that the resister has 

 become strongly compressed and that the chin-plate has 

 acquired an auricular form ; it is almost transparent, but 

 possesses a chitinised margin. The lever, it will be observed, 

 has suffered no reduction. 



Fig. 31b illustrates diagrammatically the external and 31c 

 the dorsal aspect of the organ, the atrium being separated from 

 the closing apparatus. These two figures are designed to show 

 what happens in the case of spiracle III of the male and 

 spiracles III to Xof the female, the Avhole of the atrium being 

 thrown off excepting the chin-plate and resister. This leaves 

 the interior .surface of the chin-plate exposed on the body 

 surface and also the anterior edge of the lever, so that these 

 parts now form the valvular pore or stigma. The resister is 

 further reduced and forms one edge of the mouth of the 



